The present invention relates to a device for generating light signals.
A great number of devices for generating light signals are used world-wide, for example, for traffic control as traffic lights, and exclusively using the same basic principle: the switchable surfaces of different color, for example red, yellow and green, are generated by mounting in each case at least one active, intensely radiating light source behind a correspondingly colored filter disc. The surfaces respectively switched shine in the corresponding color, while the non-switched surfaces remain dark.
This concept has a number of defects:
The light sources used have to be extremely bright so that the switched surfaces can be distinguished from the non-switched ones reliably even in bright daylight. The necessary requirement for electric power is correspondingly high.
Despite these very bright light sources, the problem of certain distinguishability is not completely and reliably solved: in the case of direct, virtually perpendicular solar irradiation onto the lights, that is to say, the low morning or evening sun, the brightness of the (additionally) actively illuminated surface cannot be distinguished from the remaining surfaces illuminated only by the sun.
The extreme brightness, mandatory for distinguishability during the day, of the light sources, is much too high at night and leads to dazzling of the car driver, particularly in the case of traffic lights which are set up outside built-up areas on unlit streets.
Intensive light sources must be changed frequently, since they have only a limited service life. Moreover, the individual service life fluctuates greatly from specimen to specimen, and no warning of the imminent total failure of the light source is generally given. The functional reliability of the lights can be raised only with an increased outlay on maintenance and material consumption.
These disadvantages are generally known. Recent inventions relating to traffic lights are therefore concerned with one or more of these disadvantages. U.S. Pat. Nos. 4,293,796 and 4,104,562 disclose electronic methods and devices for reducing the lamp brightness at night. U.S. Pat. No. 3,968,395 discloses the use of two-filament lamps in traffic lights with the aim of raising the functional reliability. U.S. Pat. No. 5,898,389 discloses a method and a device for automatically switching over to battery operation in the event of failure of the external power supply.
The object according to the invention is to provide a device for generating light signals which, firstly, can be read correctly in all environmental conditions and, secondly, requires little maintenance and energy and is cost-effective.
The object according to the invention is achieved by means of a device containing a housing with at least one opening, which is closed by a plate, the absorption of which can be controlled electrically, there being located in the interior of the housing behind the opening a diffuser element, which reflects incident light through the plate.
As such, the invention relates to a device for generating light signals comprising: (a) a housing having an interior and at least one opening, (b) at least one plate having an absorption that is electrically controllable and closing the at least one opening, and (c) a diffuser element for reflecting incident light through the plate and located in the interior of the housing behind the at least one opening.